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The Anthropocene epoch

Undeniably, our species has shaped the Earth’s environment, and our first forays into near Space may expand our influence significantly, perhaps even later this century. But will geologists of the far future look back through the strata and see the present period as being quite different from what went before? That is the question which is being addressed by the Subcommission on Quaternary Stratigraphyunder the auspices of the International Union of Geological Sciences.

The term Athropocene was coined at the turn of the century and is used generally to designate the period over which humans have had a major impact. It has been introduced because the understanding among geologists is that future members of their profession examining rock strata in thousands of years’ time would find a change in the nature of what they discover at around this point. The argument now is about exactly when to date this new epoch, which in turn relates to what the major impact of our species will be seen to have been many years hence.

This could, for example, be an abrupt change in the fossil record. We know that many species have now disappeared because they were either hunted to extinction or their habitat was destroyed (albeit, we can’t necessarily take all the blame, as some of these may have been on their way out without our help). Alternatively, our presence could be signalled by the existence of radioactive fallout from nuclear explosions in the atmosphere, or the occurrence of quantities of plastic waste. And there will certainly be other suggestions.

Inevitably, divisions such as this are themselves defined by our own understanding, but the boundaries of earlier time periods are based on clearly-discernible features evident in the geological record. Perhaps the place to start is with a look back at other recent geological epochs.

First, a brief note about terminology. Geological time is defined in terms of a number of divisions and sub-divisions. Thus, we are currently in the Quaternary Period of the Cenozoic Era of the Phanerozoic Eon. The Quaternary period started nearly 2.6 million years ago with the start of glaciation in the Northern Hemisphere and is characterised by a series of Ice Ages. It is during this period – just a blink of an eye in geological terms, with the Earth being more than four billion years old – that humans evolved.

The Quaternary period is itself sub-divided into two Epochs, the Pleistocene followed by the present Holocene epoch, dated from about 11,700 years ago and being the time in which human culture has developed from life in bands of hunter/gatherers into the sophisticated modern societies supporting a vastly greater population.

We should note that these geological sub-divisions are not (excuse the pun) set in stone. The start of what is now regarded as the Pleistocene was once considered part of the previous Pliocene epoch. Although there are clear changes in rock strata at different times, the divisions are defined by us. What is clear, though, is that the mid-Pliocene was a warm period, with temperatures 2-3° higher than at present and sea level around 25 metres higher.

This gave way to the colder Pleistocene, with its severe glaciations reaching down across much of Europe. Conditions fluctuated and what we now know as the Stone Age developed. Glaciation caused large drops in sea level and the appearance of land bridges, resulting ultimately in the spread of humans to the Americas as well as more localised impacts on the movement of our species.

The Holocene dates to the end of the 800-year period of cold in the northern hemisphere known as the Younger Dryas. As this ended and the world once again warmed, the conditions were right for Homo sapiens to flourish. Farming evolved, allowing permanent settlements to be established and grow; the rest is, quite literally, history.

In the ensuing period, humans have become by far the dominant species and have made their mark indelibly on this planet. Forests have been cleared, land ploughed or given over to grazing, some terrestrial animals and birds hunted to extinction and every continent settled. This benign split second of geological history, which we have dubbed the Holocene, has made all this possible.

The question now is whether geologists in the distant future would recognise the present day as the start of another distinct epoch or simply a continuation of the Holocene. Given the moving of the boundary between the Pliocene and the Pleistocene by a few hundred thousand years, it is clear that this is a matter of judgement rather than objective fact.

In the present case, the move to declare the start of the Anthropocene is in some ways a political act which chimes with the belief of the Deep Greens that humans are an unwelcome presence whose impact on the environment is largely negative. In this view, it seems only natural to mark our presence out as a distinct part of geological time. This is a unique situation for geologists who up till now have sought to compartmentalise what to us is the distant past.

This debate makes no difference to real life and can only sensibly be settled by generations far in the future. In the meantime, as objective as the exercise may seem to be, the dawn of the Anthropocene is to a large extent an opportunity to berate ourselves in a sort of geological mea culpa. Species extinction? Tick. Nuclear fallout? Tick. Climate change? Tick.

But perhaps the hypothetical future geologists will note instead the widespread remains of major cities and sophisticated transport networks. In the meantime, we continue to make imperfect progress and change our environment, but, just as we are the only species with a planetary-wide impact, so are we the only one that consciously tries to maintain what we understand to be a healthy environment.